Method and circuit arrangement for synchronizing plural oscillators

ABSTRACT

A circuit arrangement includes a first phase locked loop to generate a first oscillator frequency, a second phase locked loop to generate a second oscillator frequency, a reference frequency emitter connected to a reference frequency input of both phase locked loops, and a signal attenuator and optionally a switch connected between a master signal output of the first (master) loop and an input of the second (slave) loop. In a method, a common reference frequency is provided to both loops, the first loop generates a first oscillator frequency, and the second loop generates a second oscillator frequency that matches the first oscillator frequency in at least one operating mode and optionally differs from the first oscillator frequency in another operating mode. The frequency matching in one of the modes involves feeding an attenuated signal from the first loop operating as a master into the second loop operating as a slave.

PRIORITY CLAIM

This application is based on and claims the priority under 35 U.S.C.§119 of German Patent Application 103 54 521.2, filed on Nov. 14, 2003,the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to both a method and a circuit arrangement forgenerating a first oscillator frequency with a first phase locked loopand a second oscillator frequency with a second phase locked loop,wherein the second oscillator frequency may be matched to the firstoscillator frequency.

BACKGROUND INFORMATION

Various methods and a circuit arrangements of the above mentionedgeneral type are conventionally known. Such methods and circuitarrangements are utilized, for example, in the field of mobile receptionof radio signals, such as in modern automobile radios, whereby variousspecific techniques are used, in order to ensure an uninterrupted andinterference-free reception of the radio signals even under continuallychanging reception conditions.

A first example of the above mentioned techniques is given by the RadioData System (RDS), which provides for the transmission of informationindicating an alternative frequency on which the same radio program canbe received if there is interference on the primary frequency. Based onthis information indicating one or more alternative frequencies, thereceiver can monitor and evaluate the reception quality available on thevarious alternative frequencies, and then select the best frequency,i.e. the frequency with the best reception quality, for carrying out thefurther signal reception. In that context, it is advantageous to provideand operate not only a first receiver (the audio receiver) but also anadditional second receiver (a background receiver) that runs in thebackground in order to monitor and test or evaluate the receptionquality of the available alternative frequencies on an ongoing basis. Ifsuch a background receiver indicates an alternative frequency having abetter reception quality than the frequency presently being used by theaudio receiver, then the audio receiver is switched over to this betteralternative frequency. As a further possibility, the respective roles ofthe audio receiver and the background receiver are switched, namely thereceiver previously operating as the background receiver will nowoperate as the audio receiver on the alternative frequency having thebetter reception quality, while the previous audio receiver will thenoperate as the background receiver on the other frequency orfrequencies.

Continuously varying or changing reception conditions are also the causeof so-called multi-path interferences. This term applies to interferencethat arises from the superposition of signal components reaching thereceiver antenna via a direct path with other signal components thatreach the antenna via other indirect paths, e.g. due to reflections, andthus exhibit a phase shift. For example, such reflections arise on largebuildings and the like. The overall signal arriving at the antenna thusincludes multiple signal components that have reached the antenna bydifferent paths, e.g. due to different interposed reflections, and thushave different phase shifts relative to each other. Due to suchmulti-path interference, the reception can vary very strongly ordrastically over very small spatial distances due to the differingsuperposition of the various phase-shifted radio signal components.Thus, as the receiving antenna moves, the overall received signal willfluctuate or vary drastically. In this context, a second example of theabove mentioned techniques comes into play, particularly with aso-called antenna diversity system. Such a system is characterized byproviding plural antennas, and selecting a respective active antennaamong the available antennas at any time based on the signal receptionquality of the respective antenna.

A combination of the above two techniques is given, for example, by anarrangement including plural separate antennas and plural separate audioand background receivers, which are respectively coupled with their ownantennas. In such an arrangement or configuration, the specialrequirement arises, that the various receivers must operate completelyindependently of one another in a first operating mode or condition, butmust operate on the same frequency in a second operating mode orcondition. For example, in the first operating mode, one receiveroperates on the audio frequency that has been selected for the superiorreception quality thereof, while the other receiver operates as thebackground receiver and periodically tests the reception qualityavailable on the various alternative frequencies.

Moreover, in principle it is possible to operate plural receivers on thesame frequency, and to increase the signal reception sensitivity of theoverall system through the phase-correct addition of the several signalsor signal components received respectively by several antennas of theoverall system. This increase of the sensitivity can be achieved becausethe noise signals arise in an uncorrelated manner via the severalantennas, while the useful signal (e.g. the audio signal that is to bereceived) arises in a correlated manner via the several antennas.Through appropriate phase shifting of the added signals, a directionaleffect of the overall antenna system can be achieved.

In typical conventional signal superimposing receivers, e.g. heterodynereceivers, a high frequency reception signal is superimposed or mixedwith an oscillator signal so as to be mixed down to an intermediatefrequency. In this context, it is problematic that the respective localoscillators of the various receivers must be very strongly decoupledfrom one another in order to avoid mutual influence therebetween. Ingenerally known conventional methods and circuit arrangements, variousdifferent local oscillators are synchronized on a common referencefrequency, and it is attempted to decouple the local oscillators fromone another. However, phase noise of the oscillators as well as noisecomponents of the phase locked loops prevent a complete or perfectsynchronization of the oscillators when all of the oscillators are tooperate on the same frequency. Moreover, an incomplete decoupling of theoscillators relative to one another leads to a mutual or interactiveinfluence therebetween, which is noticeable as interfering noise in thereceiver.

Alternatively, a synchronization can also be achieved in that onereceiver distributes the signal of its oscillator to the otherreceivers. The local oscillators of the other receivers are thenswitched off, because the other receivers will instead use theoscillator signal provided by the first or master receiver. Thisalternative, however, requires relatively complicated and expensive highfrequency switches, in order to ensure an adequate or sufficiently highdecoupling in the switched-off condition. Since a tuning voltage fromthe phase locked loop of a local oscillator is used for adjusting ortuning subsequent or following filter circuits of the receiver, for thispurpose the tuning voltage from the phase locked loop of the activelocal oscillator must also be delivered further on to the otherreceivers, which is complicated with respect to the necessary circuitarrangements therefor. Moreover, the tuning adjustment or balancing ofthe individual receivers is complicated, since an adjustment orbalancing of the filter circuits is based on the control voltage of theoscillator (e.g. voltage controlled oscillator VCO). Thus, the tuningadjustment or balancing must occur in the entire or overall system, whenboth voltage controlled oscillators (both the internal and externalmaster oscillator) are present. In this regard, the filter balancing isfurther made more difficult if the individual receivers are respectivelysubjected to different surrounding environmental temperatures, such thatthe several receivers will exhibit different temperature-dependentcharacteristic behaviors.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the present invention toprovide a method and an apparatus for synchronizing plural oscillators,through the use of a simple and economical circuit technology and asimple or uncomplicated filter tuning or balancing. The inventionfurther aims to avoid or overcome the disadvantages of the prior art,and to achieve additional advantages, as apparent from the presentspecification. The attainment of these objects is, however, not arequired limitation of the claimed invention.

The above objects have been achieved according to the invention in amethod for generating a first oscillator frequency with a first phaselocked loop and generating at least a second oscillator frequency withat least one second phase locked loop, wherein one and the samereference frequency, i.e. a single common reference frequency, isprovided to both the first and the second phase locked loop. The secondoscillator frequency is matched to the first oscillator frequency in atleast one operating mode. Optionally, the second oscillator frequencydiffers or deviates from the first oscillator frequency in at least oneother operating mode. Further particularly according to the invention,the tuning or matching of the second oscillator frequency to the firstoscillator frequency in at least one operating mode comprises a step offeeding an attenuated signal out of the first phase locked loop into theat least one second phase locked loop.

The above objects have further been achieved according to the inventionin a circuit arrangement that is suitable for carrying out the inventivemethod. This circuit arrangement comprises a first phase locked loopadapted to generate a first oscillator frequency, at least one secondphase locked loop adapted to generate at least one second oscillatorfrequency, a single reference frequency emitter having a referencefrequency output connected in common to respective reference frequencyinputs of both the first phase locked loop and the at least one secondphase locked loop, and a circuit connection including an attenuatorconnected between the first phase locked loop and the at least onesecond phase locked loop and adapted to feed an attenuated signal out ofthe first phase locked loop into the at least one second phase lockedloop. Thereby, the circuit arrangement is adapted to match the secondoscillator frequency to the first oscillator frequency in at least oneoperating mode of the circuit arrangement.

While the attenuated signal out of the first phase locked loop is beingfed into the second phase locked loop, the first phase locked loop actsas a master and the second phase locked loop acts as a slave. In thisoperating mode or condition, the second phase locked loop operates as aresonance amplifier, which amplifies, in a phase-correct or matchedmanner, the weak injected signal of the first phase locked loop. Therebyit is ensured that both phase locked loops and their respective localoscillators will operate with the same frequency, namely the frequencyspecified by the attenuated signal provided from the first phase lockedloop and particularly the local oscillator of the first phase lockedloop.

It is preferred in one embodiment that a frequency divider of the atleast one second phase locked loop is synchronized with a frequencydivider of the first phase locked loop. This is preferably achieved bymeans of a setting device or synchronizer, which synchronizes thefrequency divider of the second phase locked loop with the frequencydivider of the first phase locked loop. This embodiment excludes thepossibility of a phase shift that could otherwise possibly arise betweenthe injected signal from the first phase locked loop and the outputsignal of the second phase locked loop.

According to a further preferred embodiment of the invention, afrequency divider of the at least one second phase locked loop issynchronized with the reference frequency. This embodiment is alsopreferably realized through the use of a setting device or synchronizer,which synchronizes a frequency divider of the at least one second phaselocked loop with the reference frequency. This embodiment represents analternative manner of excluding or avoiding a phase shift between theinjected signal and the output signal of the second phase locked loop.

It is further preferred that the first oscillator frequency issuperimposed on a reception spectrum in a first heterodyne receiver, andthereby transforms or converts a first reception frequency to anintermediate frequency. Similarly, at least one second oscillatorfrequency is preferably superimposed on the reception spectrum in atleast one second heterodyne receiver and thereby transforms or convertsat least one second reception frequency to an intermediate frequency. Acorresponding circuit arrangement preferably comprises a firstheterodyne receiver with a first mixer that superimposes or mixes thefirst oscillator frequency with a reception spectrum and therebytransforms the first reception frequency to an intermediate frequency.This circuit arrangement additionally comprises a second heterodynereceiver with a second mixer that superimposes or mixes a secondoscillator frequency with the reception spectrum and thereby transformsthe second reception frequency to an intermediate frequency. Throughthese embodiments, the reception quality is significantly improved inthe mobile reception of radio signals, for example in modern automobileradios. As a result, audible fluctuations of the reception quality arereduced, even under continuously varying or changing receptionconditions.

A further preferred feature is that at least two heterodyne receiversare coupled with respective antennas that are separated from oneanother. Such a coupling of an antenna diversity arrangement with areceiver or tuner diversity arrangement combines the advantages of tunerdiversity with the advantages of antenna diversity. For example, antennadiversity is especially suitable for compensating and thus overcoming oravoiding multi-path interferences. In this context, the plural receiverscan all operate on the same frequency.

A further preferred embodiment is characterized by a mixer thatsuperimposes, in a phase-accurate and additive manner, the respectivesignals of plural antennas that are separated from one another, eitherbefore or after a signal processing of these signals. Thereby, namelythrough the phase-accurate or phase-correct addition of the signalsrespectively received via different antennas, the total sensitivity ofthe overall system is increased.

The circuit arrangement preferably further comprises a controllablephase shifter that achieves a controllable phase shifting between thesignals that are to be superimposed. Through such a phase shifting ofthe added signals, a directional effect of the total antenna system isachieved.

It is still further preferred that the circuit arrangement comprises atleast one further heterodyne receiver with a further mixer, whichsuperimposes or mixes a further oscillator frequency with a receptionspectrum and thereby transforms a further reception frequency to anintermediate frequency and which is driven or operated with the firstoscillator frequency in a second operating mode. This embodiment makesit possible, for example, to simultaneously test plural alternativefrequencies or to sequentially sample plural alternative frequencies,while other antennas are driven with a common frequency in order toachieve a directional effect.

It should be understood that the embodiments, features and advantages ofthe invention described above and to be described below are not limitedto the particular combinations as described, but instead can also beused in other combinations or individually while still remaining withinthe scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be clearly understood, it will now bedescribed in connection with example embodiments thereof, with referenceto the accompanying drawings, wherein:

FIG. 1 is a schematic functional block diagram showing the generalfunctional block structure of a first example embodiment of theinvention;

FIG. 2 is a basic equivalent circuit diagram of a voltage controlledoscillator with an input feed of an attenuated signal, to be used, forexample, in the embodiment according to FIG. 1;

FIG. 3 is a graphical diagram of the course or curve of the amplitude ofa signal output by the voltage controlled oscillator according to FIG. 2over the frequency of the attenuated excitation signal being fed intothe oscillator;

FIGS. 4A, 4B, 4C, and 4D respectively show the time course of foursignals in connection with a synchronization of two phase locked loops;

FIG. 5 is a schematic functional block diagram showing the generalfunctional block structure of a second example embodiment of theinvention; and

FIG. 6 is a simplified block diagram of an example embodiment withplural heterodyne receivers and plural antennas.

DETAILED DESCRIPTION OF A PREFERRED EXAMPLE EMBODIMENT AND OF THE BESTMODE OF THE INVENTION

FIG. 1 schematically shows the overall construction of a circuitarrangement 10 according to the invention, having a first phase lockedloop 12 that provides a first oscillator frequency at a first output 16of the arrangement 10, and a second phase locked loop 14 that provides asecond oscillator frequency at a second output 18 of the arrangement 10.The first phase locked loop 12 comprises a first oscillator 20, forexample embodied as a voltage controlled oscillator (VCO) 20. At itsoutput 22, the first oscillator 20 provides an alternating voltagesignal having a frequency (i.e. the first oscillator frequency) that isdependent on the value of a control voltage that is provided to an input24 of the first oscillator 20. The alternating voltage signal of thefirst oscillator 20 is provided to the first output 16, and is furtherprovided to a first controllable frequency divider 26, by which thefrequency of the alternating voltage signal is divided down to the levelof a reference frequency provided by a reference frequency emitter 28.

Both the reference frequency provided by the reference frequency emitter28 as well as the divided frequency of the first oscillator 20 as outputby the first controllable frequency divider 26 are respectively providedto a first phase/frequency detector 30, where these two frequencies arecompared with one another. The first phase/frequency detector 30produces an output signal whenever the frequency and/or phase angles ofthe two signals input to the detector differ from one another. Dependingon whether the signal transitions or flanks of the divided VCO signalprovided through the frequency divider 26 lead ahead of or lag behindthe transitions or flanks of the reference signal provided by thereference frequency emitter 28, the phase/frequency detector 30 willcorrespondingly produce control signals having respective opposite signs(plus and minus, or up and down). This control signal output by thephase/frequency detector 30 is provided to a charge pump 32, whichcorrespondingly charges or discharges a capacitor, for example, inresponse to and dependent on the control signals. The voltage of thiscapacitor is provided via an output 34 of the charge pump 32 through afirst loop filter 36, which smooths this voltage to produce a controlvoltage that is provided to the control input 24 of the first voltagecontrolled oscillator 20.

The second phase locked loop 14 has an analogous structure as the firstphase locked loop 12. Thus, the second phase locked loop 14 comprises asecond oscillator 38, a second controllable frequency divider 40, asecond phase/frequency detector 42, a second charge pump 44, and asecond loop filter 46 connected in sequence to form the loop. The secondoscillator 38 produces an alternating voltage signal (with the secondoscillator frequency) at its output 48, which is provided to the secondoutput 18 and to the second frequency divider 40. The frequency of thisalternating voltage signal is dependent on the magnitude of the controlvoltage provided to the control input 50 of the second oscillator 38from the second loop filter 46.

The circuit arrangement 10 further comprises a controller 52 with anexternal input 17, an attenuating device or attenuator 54, a switch 56,and a phase synchronization device or phase synchronizer 58. Thecontroller 52, for example, adjusts or sets the divider ratios for thecontrollable frequency dividers 26 and 40 by suitable control signalsprovided thereto, and thereby controls a synchronization of the twofrequency dividers 26 and 40. Such a synchronization is triggered whenthe circuit arrangement 10 is to be set into the correspondingsynchronized operating mode, by a super-ordinated controller (not shown)that applies a trigger signal to the external input 17 of the circuitcontroller 52.

The phase locked loops 12 and 14 run or operate independently of oneanother, as long as their respective frequency dividers 26 and 40 areset to different frequencies. The circuit controller 52 controls theswitch 56, the phase synchronizer 58, and the two frequency dividers 26and 40. Under certain circumstances it can be advantageous if thedivider 26 and/or the divider 40 provide a return signal back to thecircuit controller 52, as indicated by the dashed line arrows extendingfrom the divider blocks 26 and 40 back to the circuit controller 52 inFIG. 1. From these optional return signals, the circuit controller 52can detect and recognize the current actual existing condition or stateof the respective frequency dividers 26 and 40 and accordingly wait forthe correct time window.

If both phase locked loops 12 and 14 are to provide equal frequencies attheir respective outputs 16 and 18, then the circuit controller 52adjusts both frequency dividers 26 and 40 to the same nominal or desiredfrequency. Additionally, the circuit controller 52 closes the switch 56,which thereby feeds an attenuated signal of the first oscillator 20 intothe second phase locked loop 14. The signal of the first oscillator 20in this context is attenuated by a signal attenuating device orattenuator 54 that is connected in series with the switch 56 between thefirst oscillator 20 and the second oscillator 38. The attenuator 54 maybe embodied simply as an ohmic resistance or resistor. The signal of thefirst oscillator 20 that is to be attenuated and fed to the secondoscillator 38 can be the alternating voltage signal provided at theoutput 22 of the first oscillator 20 or a different signal derivedtherefrom.

As long as the frequency of the second phase locked loop 14 deviatesstrongly or sharply from the nominal or desired frequency, then thesecond phase locked loop 14 operates in a normal operating mode, inwhich its voltage controlled oscillator 38 gradually and progressively“pulls-in” or transiently oscillates toward and then locks-in to thenominal desired frequency. When the frequency of the second phase lockedloop 14 approaches the frequency of the first phase locked loop 12, thenthe second phase locked loop 14 will synchronize itself to the frequencyof the first phase locked loop 12 due to non-linear effects in theoscillator 38 of the second phase locked loop 14. In this operatingmode, the second phase locked loop 14 operates as a resonance amplifierand amplifies the attenuated injected signal of the first oscillator 20.In this manner it is ensured that both oscillators 20 and 38 runsynchronously with the same frequency.

If the frequency of the injected signal deviates from the resonancefrequency of the second phase locked loop 14, then a phase shift willarise between the injected signal and the output signal of the secondphase locked loop 14. This phase shift is removed or set to a prescribedvalue by the phase synchronizer 58, which is also operated andcontrolled by the circuit controller 52.

It should be understood that the individual blocks shown in FIG. 1respectively have certain functions allocated thereto as describedabove. Thus, each block can concretely be embodied or comprised of oneor more circuit elements which may have any conventionally knownconstruction and arrangement for achieving the respective describedfunction. The functional blocks of FIG. 1 can also be understood asrepresenting individual steps of a method according to the invention,whereby all of the blocks shown in FIG. 1 together represent an exampleembodiment of the overall method. Analogous considerations apply to thesubject matter of FIGS. 5 and 6.

FIG. 2 shows an equivalent circuit diagram of the basic functional orcircuit elements making-up the second voltage controlled oscillator 38having an input feed of an attenuated signal from the first oscillator20 as described above in connection with FIG. 1. The oscillator 38generally comprises a passive resonant circuit 66 and an activeoscillator circuit 68, which, in an idealized case, can be representedsimply by an amplitude-dependent negative resistance 70. In this regard,a negative resistance is understood to refer to any circuit with alinear current-voltage characteristic, which does not dissipate energy,but rather provides energy upon the application of a voltage thereto.Thus, in effect, this functions as a negative resistance value. On theother hand, the passive resonator or resonant circuit 66 may, forexample, be constructed as a parallel oscillating circuit of aninductance (or concretely an inductor) 72 and a capacitance (orconcretely a capacitor) 74, which is damped by a damping resistance (orconcretely a damping resistor) 76.

If the negative resistance 70 over-compensates the positive resistanceof the damping resistor 76, then an exponentially increasing oscillationwill arise at the resonance frequency in the resonant circuit 66,whereby this oscillation is excited by the inherent internal noise ofthe circuit. The amplitude of this oscillation will continue to increaseuntil the magnitude of the negative resistance value of the negativeoscillator resistance 70 has adjusted itself (along its e.g. linearcharacteristic) to the positive damping resistor 76. Thereafter, theoscillation amplitude will remain constant. Furthermore, in FIG. 2, thealternating voltage source 77 equivalently represents the excitation ofthe oscillator 38 by an attenuated signal that is coupled out of thefirst phase locked loop 12 and into the second phase locked loop 14, forexample via the switch 56 and attenuator 54 as described above inconnection with FIG. 1.

FIG. 3 shows a theoretical curve 78 of the output voltage V of thesecond oscillator 38 with respect to, i.e. as a function of, theexcitation frequency f, as the output voltage V would arise for aconstant amplitude of the attenuated input feed signal and with a linearsuperposition of the signals. A frequency capture or pull-in range 79 ofthe oscillator 38 is defined between the two frequencies f_(u) and_(of). Between these two limit frequencies, the amplitude of the outputvoltage V is greater than an oscillation amplitude 80 of thefree-oscillating or free-running oscillator 38. In other words, in thisfrequency capture or pull-in range 79, the value of theamplitude-dependent negative resistance 70 is greater than theresistance value of the resonance damping resistor 76, which has as aresult, that the inherent self-oscillation is suppressed. It can beeasily recognized that the frequency capture or pull-in range 79 becomeslarger as the amplitude of the injected attenuated signal increases. Inthe opposite sense, a signal that lies close to the resonance frequencyf_(res) can bring about the same effect with a very small amplitude thatlies only slightly above the noise level. These circumstances make itnearly impossible to decouple the oscillators 20 and 38 without the useof a controllable switch 56.

If the frequency of the injected signal deviates from the resonancefrequency of the second phase locked loop 14, then a phase shift willarise between the injected signal and the output signal of the secondoscillator 38. In order to ensure that both frequency dividers 26 and 40are in phase, the second controllable frequency divider 40 of the secondphase locked loop 14 must be synchronized with the first controllablefrequency divider 26 of the fist phase locked loop 12. Various differentpossibilities for achieving such synchronization will be discussed infurther detail below with reference to FIG. 4 including FIGS. 4A, 4B, 4Cand 4D.

FIG. 4A shows an output signal 82 of the first controllable frequencydivider 26. Corresponding thereto, FIG. 4B shows an output signal 84 ofthe reference frequency emitter 28, and FIG. 4C shows an output signal86 of the second controllable frequency divider 40. FIG. 4D shows acontrol signal 88 output by the circuit controller 52 to the phasesynchronizer 58 in order to carry out a synchronization as mentionedabove. Note that FIGS. 4A to 4D show the respective time progressions ofthe signals 82, 84, 86 and 88, aligned with one another in time. In thisexample embodiment, the synchronization is carried out upon theoccurrence of a high signal level 90 of the control signal 88 shown inFIG. 4D.

For example, the synchronization can be achieved through a one-timeresetting of the second controllable frequency divider 40 having theoutput signal 86, after the occurrence of the high signal level 90,synchronously to the output signal 82 of the first frequency divider 26.This is represented by the arrow 92 showing the synchronization of apulse of the signal 86 with a pulse of the signal 82 falling within therange of the high signal level 90. In other words, while the pulses ofthe signals 82 and 86 are not synchronized with one another before theoccurrence of the high signal level 90 of the control signal 88, oncethe high signal level 90 occurs, the second frequency divider is resetand restarted so that its output 86 will have its pulses synchronized tothe pulses of the output signal 82 of the first frequency divider 26thereafter.

Alternatively, a synchronization timing or reset information could betaken from the output signal 84 of the reference frequency emitter 28,as indicated by the arrow 94. In other words, in this alternative, thesecond frequency divider 40 is reset and restarted so that its outputsignal 86 becomes synchronized to the cycles of the output signal 84 ofthe reference frequency emitter 28 once the high signal level 90 of thecontrol signal 88 occurs. This alternative can especially be used in thesteady-state or settled oscillating condition of the first phase lockedloop 12.

It should further be understood that, instead of a resetting orsynchronizing to the same time point (without any phase shift oroffset), it is alternatively possible to reset or synchronize to arespective time point exhibiting a prescribed phase shift between thesignals 86 and 82 or the signals 86 and 84. In other words, while FIGS.4A to 4D show a phase-matched synchronization, it is alternativelypossible to provide a phase-offset or phase-shifted synchronization.

The first embodiment of the synchronization between the signals 82 and86, as represented by the arrow 92 between FIGS. 4A and 4C, is realizedthrough the subject matter of FIG. 1, especially the connection of thesynchronizer 58, as described above. On the other hand, the secondembodiment of the synchronization between the signals 84 and 86, asrepresented by the arrow 94 between FIGS. 4B and 4C, is realized throughthe subject matter of FIG. 5, especially the connection of thesynchronizer 58, to be described next.

In this regard, FIG. 5 represents an alternative example embodiment of afunctional block structure according to the invention. While theembodiment of FIG. 5 shares much of the subject matter of FIG. 1,whereby corresponding elements are labeled with the same referencenumbers and a redundant description thereof is omitted here, theembodiment of FIG. 5 further includes additional elements or features asfollows. Particularly, the embodiment according to FIG. 5 differs fromthat of FIG. 1 through the addition of functional blocks 96 and 98allocated to the first phase locked loop 12, and functional blocks 100and 102 allocated to the second phase locked loop 14. Also, in thisembodiment of FIG. 5, the phase synchronizer 58 is connected between thereference frequency emitter 28 and the second frequency divider 40, soas to synchronize this second frequency divider 40 with the referencefrequency, rather than directly with the output of the first frequencydivider 26, as was the case in the embodiment of FIG. 1.

In this example embodiment, the blocks 96 and 98 representcharacteristic parameter fields, or concretely, memory elements storingfields of characteristic values or parameters, which are addressed withthe tuning voltage of the first oscillator 20 from the first phaselocked loop 12, and in which tuning voltages for various tuning circuitsin a first receiver 104 are stored as functions of parameters x, p_(m1),p_(m2), . . . p_(mn). These parameters are essentially dependent on thetolerances of the particular circuit elements or components being usedin the circuit. The tuning voltages of the first receiver 104 areprovided via outputs 105 of the characteristic value memories 96 and 98for the further processing of these tuning voltages in subsequent filtercircuits or stages.

Analogously, the blocks 100 and 102 can represent characteristicparameter fields, or concretely memory elements storing fields ofcharacteristic values or parameters, which are addressed with the tuningvoltage of the second voltage controlled oscillator 38 of the secondphase locked loop 14, and in which tuning voltages for various tuningcircuits of a second receiver 106 are stored. The tuning voltages of thesecond receiver 106 are provided via outputs 107 of the memory elements100 and 102 for the further processing thereof in subsequent filtercircuits.

Under the limiting or boundary condition that the same circuitcomponents are used in the resonance circuits of the voltage controlledoscillators 20 and 38 as in the tuning circuits, a temperaturecompensation is ensured when the components are arranged in spatialproximity to each other, i.e. so that they are respectively exposed tothe same surrounding environmental temperature, because the voltagecontrolled oscillator 20 or 38 is automatically tuned or compensatedrespectively by the first or second phase locked loop 12 or 14.

FIG. 6 schematically represents an example embodiment of an antennadiversity arrangement, further in connection with a circuit arrangementincluding the first and second receivers 104 and 106 according to FIG.5, for example. The signal received by a first antenna 108, ifapplicable after being amplified through an amplifier with a low noisecomponent (not shown), is provided to a mixer 110, to which the signalof the first output 16 of the first phase locked loop 12 of the firstheterodyne receiver 104 is also provided. The output signal of the mixer110 thus represents a reception signal that has been mixed down to anintermediate frequency, whereupon this mixed-down reception signal willbe further processed in subsequent filter circuits or stages 112. Forthis purpose, the suitable tuning voltages are provided from thememories 96 and 98 to the subsequent filter circuits 112 via the outputs105 of the first phase locked loop 12 i.e. of the first receiver 104.

Analogously, the signal received by a second antenna 114, if applicableafter an amplification through an amplifier with a low noise component(not shown), is provided to a mixer 116, to which the output signal ofthe second output 18 of the second phase locked loop 14 of the secondheterodyne receiver 106 is also provided. The output signal of the mixer116, which represents the reception signal mixed-down to an intermediatefrequency, is then provided to subsequent filter circuits 118 forfurther processing. For this purpose, the suitable tuning voltages areprovided to the subsequent filter circuits 118 from the memories 100 and102 through outputs 107 of the second phase locked loop 14 i.e. of thesecond receiver 106.

Furthermore, circuit elements for setting or adjusting a controllablephase shift between the respective reception signals received via theantennas 108 and 114 can additionally be provided. For this purpose inFIG. 6, a controllable phase shifter 120 is circuit-connected into thehigh frequency portion of the receiver arrangement, whereby this phaseshifter 120 is controlled by a controller 122. Furthermore, thecontroller 122 actuates a double-throw switch 124, which selectivelyconnects and directs the signal received by the second antenna 114either to the mixer 116 as described above or to the phase shifter 120.The output signal of the phase shifter 120 is then provided to a furtheradditive mixer 126, in which the output signal of the phase shifter 120is additively combined with the signal received by the first antenna108.

Through such a superposition or heterodyning of phase-shifted signals,it is possible to achieve a directional effect of the reception antennaarrangement according to the so-called phased array principle. It shouldbe understood that the phase shifting and superposition can be carriedout not only on the high frequency plane or level upstream of themixers, but rather also on the intermediate frequency plane or leveldownstream of the mixers.

Similarly, for example, a controlled non-zero phase shifting can also beachieved by the phase synchronizer 58, which achieves a phase shift ofzero in FIG. 4 as described above, but of course is not limited to thissingular value (zero). In other words, the phase synchronizer 58,instead of achieving a synchronization with a zero phase shift oroffset, could instead achieve a synchronization with any desired phaseangle shift or offset other than zero.

As a further alternative deviating from the illustration of FIG. 6, acircuit arrangement having only a single antenna 108 could have firstand second heterodyne receivers 104 and 106 allocated to this singleantenna 108, for example as a combination of an audio receiver 104 and abackground receiver 106 in the manner discussed above. In such a case,the second antenna 114 of FIG. 6 would be omitted, and instead replacedby the dashed cross-connection line 128.

Although the invention has been described with reference to specificexample embodiments, it will be appreciated that it is intended to coverall modifications and equivalents within the scope of the appendedclaims. It should also be understood that the present disclosureincludes all possible combinations of any individual features recited inany of the appended claims.

1. A method of generating frequencies comprising: a) providing a commonreference frequency to both a first phase locked loop and a second phaselocked loop; b) generating a first oscillator frequency with said firstphase locked loop; c) generating a second oscillator frequency with saidsecond phase locked loop; and d) at least in one operating mode, feedingan attenuated signal from said first phase locked loop into said secondphase locked loop, and carrying out said generating of said secondoscillator frequency dependent on and responsive to said attenuatedsignal so that said second oscillator frequency matches said firstoscillator frequency.
 2. The method according to claim 1, furthercomprising, in another operating mode, carrying out said generating ofsaid second oscillator frequency so that said second oscillatorfrequency differs from said first oscillator frequency.
 3. The methodaccording to claim 2, further comprising not feeding said attenuatedsignal from said first phase locked loop into said second phase lockedloop in said another operating mode.
 4. The method according to claim 3,wherein said not feeding of said attenuated signal comprises opening aswitch to positively disconnect and discontinue said feeding of saidattenuated signal.
 5. The method according to claim 1, furthercomprising producing said attenuated signal by tapping or deriving amaster signal from said first oscillator frequency and then attenuatingsaid master signal to produce said attenuated signal, and wherein saidfeeding of said attenuated signal comprises providing said attenuatedsignal to an input of a voltage controlled oscillator of a said secondphase locked loop that generates said second oscillator frequency. 6.The method according to claim 1, wherein said first phase locked loopincludes a first frequency divider, said second phase locked loopincludes a second frequency divider, and said method further comprisessynchronizing said second frequency divider with said first frequencydivider.
 7. The method according to claim 1, wherein said second phaselocked loop includes a frequency divider, and said method furthercomprises synchronizing said frequency divider with said referencefrequency.
 8. The method according to claim 1, further comprisingsuperimposing said first oscillator frequency on a first receptionfrequency to thereby produce a first intermediate frequency, andsuperimposing said second oscillator frequency on a second receptionfrequency to thereby produce a second intermediate frequency.
 9. Acircuit arrangement for generating frequencies, comprising: a firstphase locked loop adapted to produce a first oscillator frequency at afirst output of said first phase locked loop; a second phase locked loopadapted to produce a second oscillator frequency at a second output ofsaid second phase locked loop; a reference frequency emitter adapted toemit a reference frequency at a reference output of said emitter that isconnected to a first reference input of said first phase locked loop andto a second reference input of said second phase locked loop; and aninterconnection including a signal attenuator connected between saidfirst phase locked loop and said second phase locked loop and adapted tofeed an attenuated signal from said first phase locked loop to saidsecond phase locked loop; wherein said second phase locked loop isadapted to produce said second oscillator frequency matching said firstoscillator frequency based on said attenuated signal in one operatingmode.
 10. The circuit arrangement according to claim 9, wherein saidsecond phase locked loop is adapted to produce said second oscillatorfrequency different from said first oscillator frequency in anotheroperating mode.
 11. The circuit arrangement according to claim 9,wherein said interconnection further includes a controllable switchconnected in series with said signal attenuator and adapted toselectively complete and interrupt said interconnection so as toselectively enable and disable the feeding of said attenuated signal tosaid second phase locked loop.
 12. The circuit arrangement according toclaim 9, wherein said first phase locked loop includes a first voltagecontrolled oscillator having a master signal output, said second phaselocked loop includes a second voltage controlled oscillator having amaster signal input, and said interconnection is connected between saidmaster signal output and said master signal input.
 13. The circuitarrangement according to claim 12, wherein said first voltage controlledoscillator further has a first oscillator output that is distinct fromsaid master signal output and that is connected to said first output ofsaid first phase locked loop, and said second voltage controlledoscillator further has a second oscillator output that is connected tosaid second output of said second phase locked loop.
 14. The circuitarrangement according to claim 12, wherein said first voltage controlledoscillator has a first main oscillator output connected to said firstoutput of said first phase locked loop, said master signal outputcorresponds to, is connected to, or is derived from said first mainoscillator output, and said second voltage controlled oscillator furtherhas a second main oscillator output that is connected to said secondoutput of said second phase locked loop.
 15. The circuit arrangementaccording to claim 12, wherein said second voltage controlled oscillatorfurther has a loop control signal input that is distinct from saidmaster signal input and that is connected in said second phase lockedloop.
 16. The circuit arrangement according to claim 9, a wherein saidsignal attenuator is an ohmic resistor.
 17. The circuit arrangementaccording to claim 9, wherein said first phase locked loop includes afirst frequency divider, said second phase locked loop includes a secondfrequency divider, and said circuit arrangement further comprises aphase synchronizer that is connected between an output of said firstfrequency divider and a synchronizing input of said second frequencydivider and that is adapted to synchronize said second frequency dividerwith said first frequency divider.
 18. The circuit arrangement accordingto claim 9, wherein said second phase locked loop includes a frequencydivider, and said circuit arrangement further comprises a phasesynchronizer that is connected between said reference output of saidreference frequency emitter and a synchronizing input of said frequencydivider and that is adapted to synchronize said frequency divider withsaid reference frequency.
 19. The circuit arrangement according to claim9, further comprising: a first heterodyne receiver incorporating saidfirst phase locked loop therein; a second heterodyne receiverincorporating said second phase locked loop therein; a first signalreception input adapted to receive a first reception frequency; a secondsignal reception input adapted to receive a second reception frequency;a first mixer that has a first input connected to said first signalreception input and a second input connected to said first output ofsaid first phase locked loop of said first heterodyne receiver, and thatis adapted to superimpose said first oscillator frequency on said firstreception frequency to form a first intermediate frequency; and a secondmixer that has a first input connected to said second signal receptioninput and a second input connected to said second output of said secondphase locked loop of said second heterodyne receiver, and that isadapted to superimpose said second oscillator frequency on said secondreception frequency to form a second intermediate frequency.
 20. Thecircuit arrangement according to claim 19, further comprising a firstantenna connected to said first signal reception input, and a secondantenna that is separate from said first antenna and connected to saidsecond signal reception input, wherein said first and second heterodynereceivers are respectively coupled via said first and second mixers tosaid separate first and second antennas.
 21. The circuit arrangementaccording to claim 20, further comprising a cross-connection including athird mixer connected between said first and second signal receptioninputs.
 22. The circuit arrangement according to claim 21, wherein saidthird mixer is interposed between said first signal reception input andsaid first mixer, in that said third mixer has a first input connectedto said first signal reception input, a second input connected to saidsecond signal reception input, and an output connected to said firstinput of said first mixer.
 23. The circuit arrangement according toclaim 22, wherein said cross-connection further includes a controllablephase shifter interposed between said second signal reception input andsaid second input of said third mixer.
 24. The circuit arrangementaccording to claim 22, wherein said cross-connection further includes acontrollable switch interposed between said third mixer, said secondsignal reception input and said first input of said second mixer, inthat said controllable switch has a switch input connected to saidsecond signal reception input, a first switch output connected to saidsecond input of said third mixer, and a second switch output connectedto said first input of said second mixer, and said controllable switchis adapted to selectively connect said switch input to said first switchoutput or said second switch output as selected.
 25. The circuitarrangement according to claim 19, further comprising a third heterodynereceiver and a further mixer that superimposes a third oscillatorfrequency of said third heterodyne receiver on a third receptionfrequency to form a third intermediate frequency in a first operatingmode, and that is operated with said first oscillator frequency in asecond operating mode.
 26. The circuit arrangement according to claim19, further comprising only a single antenna connected to said firstsignal reception input, no antenna connected to said second signalreception input, and a circuit connection between said first and secondsignal reception inputs.
 27. A mobile radio receiver apparatuscomprising the circuit arrangement according to claim 9, and furthercomprising at least one antenna and at least one mixer connected to saidcircuit arrangement.